Plant electrical signalling regulates a wide range of physiological functions including stress responses to drought and wounding. Existing tools for monitoring such signals often require the uses of cumbersome and expensive equipment in well-controlled laboratory. This project aims to create a low-cost measurement tools that can function robustly in the field, collecting electrical activity profiles from multiple plants.

The Idea

Cell-cell communication is the hallmark of multicellularity. Our understanding of how individual cells communicate and give rise to organismal-level behaviors are thus critical for engineering complex multicellular systems such as animals or plants. In animals, cell-cell communication via electrical signalling plays important roles in nervous systems, enabling fast responses to environmental stimuli. Previous studies indicate that all higher plant may also utilise electrical signalling to regulate a wide-range of physiological functions including stress responses to drought, light condition and wounding. Tools for recording and controlling plant electrophysiology could open up promising applications in diagnosis of plant pathology and modulation of plant adaption. Nonetheless, existing setups for monitoring plant electrophysiology often require the uses of cumbersome, expensive and specialised equipment on only small areas of plants in well-controlled laboratory environment. In practice, one would prefer to have low-cost measurement tools that can function robustly in the field, capture overall electrical activities of the whole plant and easily be reconfigured for various applications. Here we plan to prototype a plant electrophysiology measurement device based on open source Programmable System on the Chip (PSoC) and wireless communication system. The device should be able to operate outside laboratory environment, collect and store data for at least several days without human intervention. The measurement setup procedure should be simple enough for a layperson to learn within an hour. The design of the device should be simple and cheap enough to be mass produced for whole plant / whole field measurement. In addition, we plan to use our device for community outreach: as a tool for learning about interfacing engineering to biology and as a platform for building up a database of plant electrophysiological profile through citizen science projects. An ability to reduce cost, lower down barrier of entry and scale up plant electrophysiological research would bring us closer to realising the full application potential of this field.

Project Outputs

Summary of the project's achievements and future plans

Original proposal and application

Project Outcomes

Amplifications and wireless transmission of electrical signals from sensitive plants

Summary

We have prototyped a tool for measuring plant electrical signal coupled with radio modules for long-distance data collection. This prototype can sense and transmit signals from Venus flytrap responding to tactile inputs (see video below for demonstration). The estimated cost of the prototype is approximately £40.

Report and Outcomes

We have prototyped a plant electrical signal amplifier coupled with a radio module. We demonstrated that this prototype can sense and transmit signals from Venus flytrap action potential (pulse width ~ 1400 ms; amplitude ~ 5 mV) responding to tactile inputs. We showed that it is possible to distinguish action potential from other disturbance using post-transmission signals. The estimated cost of each of our current amplifier - radio module is approximately £40. The amplifier, based on Backyard Brain Plant Spiker Shield, consists of a high impedance instrumental amplifier AD623 and two Operational amplifiers TLC2272. All amplifiers are powered by 5V sources from an Arduino board. Signal voltage range is set between 0V and 5V with a reference voltage at 2.5V (see the diagram). We found that this reference voltage value is necessary for achieving amplification folds close to that of ideal operations. We also decided to add another instrumental amplifier AD623 to bring voltage range down to 0-2.5V in order to match the analog input range of the wireless transmitter modules (see further discussion below). We have tried adding 50 Hz second order notch filter to eliminate DC noise but the filter attenuates too much of plant signals. We found that a plain copper wire coated with electrogel is sufficient as an electrode for plant-circuit interface. However, we noticed that electrogel seemed to be toxic to plant soft tissue (e.g. traps of venus flytrap) which turned yellowish/brownish a few days after we applied the gel. Therefore, for long term monitoring of electrical signal, we should look for less toxic alternatives.

While amplitudes and durations of action potential appeared to be consistent across different experiment repeats on the same trap, there is a small difference across different traps from the same plant. More importantly, we found that any trap whose sensory hairs remain green is insensitive to touch, neither generating action potential nor closing. Such variability of sensitivity and response across different plants (or different parts of the same plant) are likely to complicate future attempts to apply plants as environmental sensors. In order to transmit the amplified signal wirelessly over a long distance, we have utilised ZigBee communication protocol using 2 programmable XBee PRO ZigBee S2 modules, with one of the modules being configured as a transmitter and the others as a receiver unit using XCTU software. The transmitter has a built-in Analog-to-Digital Converter (ADC) function, which allows the amplified plant analog signal to be converted to digital signal accordingly. The ADC function allows a rather narrow voltage input range, thus limits the range in which the amplifier can operate as previously mentioned. We have configured the transmitter to capture the signal with the highest possible sampling rate (20Hz) to minimise signal loss. This resulted in a very high power consumption of the transmitter, which is a major drawback of this setting. The receiver was connected to an Arduino board, which was pre-programmed to convert the transmitted signal into a graphical representation as well as display numerical readings on the processing software. We were able to compare the signal readings prior to transmission with that from the receiver unit. We found that there was no detectable signal loss within 5-metre communicating range. Nevertheless, the maximal communicating distance of the prototype has yet to be determined. TEPARACreportApril2016

Follow-On Plans

Possible sensor/controller improvement. A Programmable System on a Chip (PSoC) from Cypress Semiconductor will be used for analog-digital conversion. We plan to use the CY8KIT-059 PSoC® 5LP Prototyping Kit by Cypress semiconductor. The use of such prototyping kits manufactured in large batches would allow us to lower the cost (~ £7.5 total cost per kit as oppose to £20 for Arduino) and better analog to digital conversion (20 bit as oppose to 10 bit for Arduino). The PSoC is a novel programmable electrical chip that has both programmable analog and digital components. This will allow the use of just one integrated circuit to make the device. We will also expand our current wireless network work by developing an internet data logging system which will allow us to deposit processed data directly onto an online interface. To achieve this, we will incorporate an XBee wifi module into our current receiver unit design. The wifi module will enable the Internet access and allow data transmission from the microcontroller onto the online interface. We will also look for an alternative of XBee module in order to further reducing the cost of the prototype such as XRF module by Ciseco.